The present invention relates generally to improvements to the delivery of drugs, particularly to systems for subcutaneous injection/aspiration (syringes) for drug delivery providing intermittent, episodic or limited drug delivery (as opposed to continuous drug delivery of syringe pumps). More specifically, this invention relates to an improved means of subcutaneous drug (fluid) injection and aspiration, providing a means and method of controlling and monitoring the interaction of specific flow rate and pressure during fluid injection and aspiration with a hypodermic hollow-core needle. b. Description of the Prior Art
Infusion pumps devices and systems are relatively well known in the medical arts, for use in delivery or dispensing a prescribed medication to a patient. These may be compact pump housings or larger stationary pump housing units. The administration of prescribed drugs has been described in the literature as administration to a patient through infusion tubing and an associated catheter or the like, thereby introducing the drug intravenously. These systems have seen improvements over time with respect to determining infusion line occlusion. Line blockage would cause pressure in the syringe to increase. Systems in the prior art have been developed to identify a predetermined threshold or to monitor pressure to determine means for selecting ranges of occlusion pressures to insure patient safety. U.S. Pat. Nos. 5,295,967; 4,731,058; and 5,080,653 show systems (with syringe pumps or the like) which are adequate for the intended use of intravenous drug delivery and more specifically for monitoring occlusion during infusion. However, these systems do not provide a means for drug delivery subcutaneously via a hypodermic needle. Moreover these systems do not provide a means of aspiration during drug delivery, which is a medical requirement for subcutaneous injection in an attempt to avoid intravascular placement of the hypodermic needle.
Pain, tissue damage and post-op complications have long been tolerated as negative side effects from the use of existing hypodermic drug delivery injection systems. This is well documented in both the dental and medical literature. The pain and tissue damage are as a direct result of uncontrolled flow rate in conjunction with excessive pressures created during the administration of drug solutions within the tissue spaces. Subjective pain response of a patient has been demonstrated to be minimized at specific flow rates during the administration of a drug. Also, it has been scientifically demonstrated that particular pressures (excessive without occlusion, per se) for a specific tissue type will cause damage. It is therefore critical that a specific flow rate in conjunction with a specified pressure range be maintained during the delivery of fluids (drugs) when a subcutaneous injection is given preventing subjective pain response as well as tissue damage. It is also necessary that this system have the capability to aspirate under controlled conditions of rate and pressure to avoid the same negative side effects during fluid movement. U.S. Pat. No. 5,180,371 to Spinello, incorporated herein by reference, presented an invention which allowed a rate to be set for the drug via a hypodermic needle. That invention however did not disclose means of determining, detecting or monitoring pressure during the administration of a drug.
During the early 1980""s, several researchers ( See for instance Rood, The Pressure Created by Inferior Alveolar Injections, British Dental J. 144:280-282 (1978); Walton and Abbot, Periodontal Ligament Injection; a Clinical Evaluation JADA.(Oct. 1981); Smith and Walton, Periodontal Ligament Injection; Distribution of Injected Solution Oral Surg 55:232-238 (1983)} clearly demonstrated and concluded that the pressure created by the injected fluid is critical to preventing tissue damage and a pain response. Variability, different collagen types and connective tissue densities results in different tissue compliance and distensibility. These variations are found between subjects and within the individual subjects. Rood in his 1978 article states that xe2x80x9c[t]he relationship between rate of injection and pressure rise seen clearly with the smaller volumes was lost when 2.0 ml was injected. Several high pressures were recorded and some unexpected low ones. Many tracings showed a pattern suggestive of tissue disruption and it is possible that said low pressures were due to the fluid no longer being contained within the pterygomandible space as the volume injected was similar to the previously estimated volume of the tissue space.xe2x80x9d Hence, it appears that the rate of flow is not directly related to pressure during an interstitial injection.
Smith and Walton described in their article identified supra discussed above that they have performed a histologic animal study (canines) using a technique to calibrate manual pressures produced. They concluded that the xe2x80x9cVolume injected and needle location were not always related to distribution . . . Injecting under moderate to strong back pressure gave deeper and more widespread dye penetration.xe2x80x9d This once again confirms that pressure is the critical variable in the distribution of the solution within tissues and the volume is not always related to the pressure produced.
Pashley, Nelson and Pashley in xe2x80x9cPressures Created by Dental Injectionsxe2x80x9d (J Dent Res 1981) used a pressure transducer and fixed flow rate created by a motor driven traditional syringe clearly demonstrated that different tissues have a different tissue compliance. Interstitial pressure variability was statistically and clinically significant even with a fixed flow rate. Therefore, it may be concluded that they produced great variations of pressure by using a metered flow rate.
Pertot and Dejou described in their article xe2x80x9cEffects of the force developed during periodontal ligament injections in dogsxe2x80x9d (Oral Surg. Oral Med, Oral Pathol. 1992) how they used a syringe coupled to a miniature force transducer and found a positive correlation between the number of osteoclasts and the force applied on the syringe plunger, which indicated the pressure generated in the PDL space enhanced osteoclastic activity. This experiment again indicates that pressure is a critical factor to tissue damage and is dependent on the resistance encountered and not the flow rate of the solution into the tissues.
One of the goals of dentistry and medicine should be to administer care to patients in the most humane and painless manner. The sine qua non of any treatment is to produce a desired result without causing damage or pain to the individual. Therefore there is an important need in all fields of surgery for an injection system which can be used to administer a fluid while causing substantially no pain or tissue damage to the patient.
The present invention has for its objective to minimize subjective pain response and any potential tissue damage to a patient resulting from of inappropriate pressures produced during the administration of a drug via hypodermic needle.
A further objective is to provide these benefits using a variety of different drug sources, i.e., standard syringes as well as, anesthetic cartridges or carpules.
A further objective is to provide a system which can be used easily by a clinician with very minimal training.
A further objective is to provide a system of the type discussed above having a substantial disposable portion.
A further objective is a system which can provide not only injections but also proper aspiration and/or biopsy with the capability to control both rate and pressure.
A further objective is to provide a system which automatically determines and uses the exit (or entry) pressure as a control parameter for any size and combination of syringe, tube or needle.
Prior art references are known which attempt to utilize a pressure transducer to measure the pressure within the syringe (See for instance U.S. Pat. No. 5,295,967). A major deficiency of these systems is their inability to adjust the flow rate and/or pressure of the fluid to compensate for changes in resistances throughout the system, or to the exit pressure. (Exit pressure refers to the fluid pressure just downstream of the needle tip within the patient""s body). Moreover, the prior art references fail to provide any means of determining this exit pressure. The present invention comprises a microprocessor-based system which measures a pressure or force generated externally of the tissues, and then uses this measurement to accurately determine the corresponding exit pressure. In other words, by using specific software, the system monitors the exit pressure and generates and maintains a specific flow rate even when there are changes in the resistance of the system.
The invention also provides a system which automatically compensates for the total resistance encountered within the system and which has been proven to influence flow rates and measured pressure. It is believed that this is the first system which has the capability to provide a precisely defined flow rate and desired pressure by taking into account the total system resistance. It is submitted that without this capability, flow rates and exit pressures cannot be precisely derived for varying disposable assemblies consisting of different syringe, tubing, needle sizes and fluid characteristics. A critical feature of the system is that it controls and monitors the pressure using a transducer that generates a feedback parameter.
Briefly, a system in accordance with this invention for dispensing a fluid by injecting the same into a patient includes a mechanical assembly and an electrical controller. The mechanical assembly consists of a drive mechanism and a disposable portion consisting of a fluid storage device such as a syringe, a carpule and the like, and a fluid delivery section including a tube coupled to said fluid storage device and terminating in a needle adapted to be inserted into the subject tissue. The drive mechanism includes a housing with an internal motor and a mount for mounting the fluid storage device on the housing. The fluid storage device includes a reciprocating plunger. A coupling is used to move the plunger with said motor. Importantly, a transducer is used to sense the force or pressure generated by the motor and applied by the plunger within the fluid storage device. If a carpule is used for the fluid storage device, an adapter is also provided to allow the same mount to secure the carpule as well. The mount is arranged and constructed to secure syringes or carpules having a large variety of sizes. The motor, the coupling associated with the motor and the electronic controller discussed below is at least partially disposed within the housing for protection.
The electrical controller is provided for controlling the overall operation of the system. The controller includes a master microprocessor which may be provided as a standard stand-alone PC or laptop PC, and an internal slave microprocessor operating in response to commands from the master microprocessor. The master microprocessor provides the interfacing with the clinician and collects data regarding the mechanical assembly. The master microprocessor is also associated with a display used to provide instructions to a clinician and an input device, which may be a keyboard, a touch screen or voice-activated device to collect information from the clinician. The master microprocessor is further associated with a memory which holds several data banks, each data bank being associated with one of the elements of the disposable portion as well as other parameters.
The fluid storage device is filled and a setup process is initiated during which various operational parameters are calculated, retrieved or received from the clinician. The clinician also specifies the fluid flow rates and peak exit pressure and a total amount of fluid to be dispensed. Then he operates a pneumatic control such as a foot pedal and initiates the fluid flow. Alternatively, commands may be initiated by the clinician either electronically or by voice commands. During dispensing, the output from the transducer is used to calculate the current exit fluid pressure. If this exit pressure approaches a certain threshold, the fluid flow rate is automatically reduced to prevent excessive exit pressure, thereby ensuring that the patient does not suffer undue pain and no tissue is damaged. Several optional features are also provided including aspiration, purging or charging the media with or without air.
Alternatively, the system may be operated in a biopsy mode in which the entry pressure and the outbound or withdrawn fluid flow rate are the relevant control parameters.
Throughout the process, the clinician is provided with constant current information on the ongoing process, both visual and aurally, including the current flow rate, total volume ejected or aspired, exit or entry pressures and other parameters. The slave microprocessor receives commands from the master microprocessor and generates the drive signals required to operate the motor.